In edge emitting laser diodes, the carrier substrate or growth substrate of which is at least partly transparent to a radiation generated, as is the case for example, for blue or green emitting InGaN laser diodes on GaN substrates, scattered light of the laser mode and spontaneously emitted light can propagate in the substrate. If this light emerges from the coupling-out facet, which can be designated as substrate light emission, the beam quality of the emitted laser radiation decreases since the radiation no longer emerges from a single, point-like region at the coupling-out facet and, consequently, the ideal Gaussian emission characteristic of the laser is disturbed. Particularly when such laser diodes are used in laser projectors with so-called flying spot technology, the disturbing emission from the substrate gives rise to undesirable imaging aberrations in the projected image, for example, as a result of a disturbing bright and un-sharp image edge around the projected image.
In order to reduce the substrate light emission, a laser diode can be mounted for example, on a heat sink or a housing such that the coupling-out facet is offset toward the rear with respect to a front edge of the heat sink. As a result, part of the light emitted by the coupling-out facet is masked out by that part of the heat sink which is arranged in front of the coupling-out facet. However, only a small part of the substrate light emission can be reduced by this means, since said substrate light emission is emitted from the entire substrate. Moreover, the laser power, that is to say the power of the desirably emitted laser light, is also undesirably reduced as a result.